A sidestream type of gas sampling system transports a flow of gas from the patient's airway through a sampling tube, to a sample cell, where the constituents of the gas are measured by a gas sensing system. Gases are continuously aspirated through the sampling tube, and into the sample cell, which is located typically within a gas measurement instrument. Gases are commonly sampled at flow rates ranging from about 50 ml/min to about 250 ml/min.
For purposes of description, the discussion herein is focused on patient interfaces and/or cannulas for use with human patients, it being understood that the present invention is not limited in scope only to use with human patients and can beneficially be used in various other contexts. For example, the present invention may also be used in the area of veterinary medicine where the “patients” are animals.
Different types of oral/nasal cannulas are used to deliver oxygen to patients who need assistance to breathe properly, to collect a gas sample from patients to monitor respiration, or to perform both functions. Such cannulas are used when direct ventilation is not provided. The term “oral/nasal” refers to the adaptable configuration of such cannulas, which can be in close proximity to the oral cavity (mouth) or inserted into the nasal cavity (nostril(s) or nares) of the patient. In either arrangement, a sidestream of the patient's exhaled breath flows through the cannula to a gas analyzer to be analyzed. The results of this non-invasive analysis provide an indication of the patient's condition, such as the state of the patient's pulmonary perfusion, respiratory system, and/or metabolism.
Some nasal interfaces for carbon dioxide sampling are perceived failing to remain in position during monitoring and uncomfortable. Also, differences between patients, in particular, in the spacing between the patient's nostrils, and the spacing between the patient's nose and mouth, as well as differences in airflow from the nostrils should be considered.
In addition, the nasal resistance between subjects can vary significantly. As such, the nasal airflow can often be quite asymmetric between the two nostrils. This can affect the efficiency of oxygen delivery, as the delivery will depend upon the nature of an obstruction in one or both nostrils, and how the oxygen is delivered. Existing nasal carbon dioxide sampling and oxygen delivery cannulas either deliver to a single nostril, deliver equally to both nostrils, or produce a “cloud” of oxygen, which is inhaled by the subject. A simple means to preferentially direct oxygen to the less obstructed nostril is desired.
In addition to sidestream sampling techniques, the present invention also relates to various monitoring techniques. It is known that if oxygen levels in the blood become very low at peripheral sites, a variety of clinical problems may occur. In addition, diseases, acute injuries, and other conditions can adversely affect blood flow to and in the limbs, and poor blood flow reduces the amount of oxygen that is carried in the blood stream to cells.
In general, blood oxygen levels are currently measured by pulse oximetry, which can be categorized into transmittance and reflectance types. Transmittance, or transillumination oximetry, involves the process in which a sensor measures light extinction as light passes through a portion of blood-perfused tissue. Light is transmitted from one side of a portion of blood-perfused tissue, and is recorded by a detector situated on the opposite side of the same portion of tissue. Reflectance oximetry, on the other hand, has both the light source and the detector on one side of the tissue, and measures reflectance back from the tissue.
For both types of oximetry, multiple signals from the light sensor, or detector, may be used to estimate the oxygen saturation in the blood and/or pulse rate from changes in absorption of the light detected throughout blood pulse cycles. The technology is based on the differential absorbance of different wavelengths of light by different species of hemoglobin, as known in the art.
Conventional pulse oximetry measurement in certain classes of patients, for instance severely burned patients, can be a significant challenge, yet this monitoring data is vital in operating room and intensive care settings. Most current pulse oximetric approaches depend upon available peripheral sites permitting transillumination oximetry, which is sufficient for most surgical conditions and procedures. However, in some instances, such as patients with severe burns, only a few sites may be suitable for the effective placement of the transmitting pulse oximeter sensor. These patients often have severely comprised circulatory function, thereby rendering the current peripheral pulse oximeters less effective. Therefore, it is desirable to measure to measure oxygen saturation from a central measure.
With respect monitoring, a robust and inexpensive apnea monitor, for example, particularly for adults, has yet to appear on the market. In the United States, an apnea monitor is defined by the Code of Federal Regulations as “a complete system intended to alarm primarily upon the cessation of breathing timed from the last detected breath. The apnea monitor also includes indirect methods of apnea detection, such as monitoring of heart rate and other physiological parameters linked to the presence or absence of adequate respiration.” 21 C.F.R. §868.2377. An easy to apply device with robust and redundant detection methods of apneas is desired.
The present invention is further concerned with providing a simple way of performing ambulatory sleep diagnostic studies. An easy to apply single-site device that provides the ability to sense directly or surrogates of effort, SpO2, or flow is desired.